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GLIDING THROUGH THE WAVES Bill Woodward and Yann Bernard from the CLS Group discuss satellite communications for gliders
Following in the wake of ocean moorings, drifting buoys and autonomous profiling floats, gliders are exciting new tools of the in- situ ocean observing system networks. With a large payload capacity and a wide range of autonomy, these underwater vehicles use the latest satellite technologies to transmit their data, receive commands and to be recovered at sea.
Gliders enhance the ocean in-situ sampling by providing both manoeuvrability and
position control. The gliders can perform saw-tooth trajectories from the surface to depths of 1000-1500m, along programmable routes (using two-way satellite link). They can achieve forward speeds of up to 40 km/day thanks to wings and rudders, and can be operated for a few months before they have to be recovered1
“ The gliders can perform saw-tooth trajectories from the surface to depths of 1000-1500m, along programmable routes (using two-way satellite link) ”
. Gliders
record temperature, salinity, and pressure data with a Conductivity Temperature Depth (CTD) sensor. Additional sensors can be added to measure biogeochemical parameters, such as dissolved oxygen, different fluorescences and/or optical backscatters. Even passive and active acoustic instruments have successfully been used. At each surfacing, they connect to a computer on land typically via the bidirectional Iridium satellite phone system in order to send the data collected and receive new commands, every ~4-5 hours if necessary (at a rate of about 10Kbytes/minute). Iridium, a real-time system with a global and continuous coverage provides a dedicated data collection service for ocean applications like gliders with high volumes of data to transmit. Composed of 66 operational satellites this American system initially designed for voice communication is also well adapted to transmit data from ocean platforms to boats or land infrastructures.
While gliders are new high technology platforms able to carry a large variety of different types of payloads, the Argos satellite system, a GPS free location system, is also used by gliders as a back-up solution in case of emergency. Almost all gliders are fitted with an Argos transmitter and a dedicated battery source. The very
reliable Argos satellite system is able to locate an ocean platform fitted with an Argos transmitter within 250 metres of accuracy for recovery when all other communication systems are not working. With global coverage, especially fitted for harsh conditions and low power consumption applications, the Argos system is like the guardian Angel of gliders (several gliders have been already been recovered using Argos).
CLS has been a major partner with large international in-situ oceanography programmes for the last 25 years. Combined with a close partnership with the ocean platform manufacturers and a worldwide network of offices and subsidiaries, CLS offers worldwide ocean data collection and processing services for international organisations across a broad spectrum of applications. Operational 24/7, CLS manages and maintains a full set of global operational systems, including ground segments, satellite and communications networks and redundant global data processing centres. With more than 22,000 satellite platforms (Argos and Iridium systems) in operation per month CLS provides optimal one-stop shopping for glider satellite communications. With reactive and personalised customer service from a highly qualified technical support staff for both Argos and Iridium technologies, CLS provides to the glider users a dedicated satellite services to collect and localise this new generation of autonomous ocean platforms.
1 (Davis et al., 2002; Rudnick et al., 2004).
© Enrique Vidal Vijande (IMEDEA)
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